The field of this invention is inflatable structure, such as inflatable life rafts and inflatable aircraft escape slides, and methods for making such structure. More particularly, this invention relates to such inflatable structure which is especially resistant to loss of inflation integrity caused by exposure to intense radiant heat energy. Such radiant heat energy may result from an aircraft fuel fire.
Modern commercial passenger aircraft are equipped with one or more inflatable escape slides. Such escape slides are deflated and folded for storage in or adjacent to the various doors of the aircraft. After an emergency landing such slides are rapidly deployed and inflated. The aircraft passengers and crew may safely escape from the aircraft by sliding down the inflated slides to reach the earth.
Further, when an aircraft is ditched in water the passengers and crew may slide from the aircraft into the water by using the inflated slides. After the passengers and crew have escaped from the aircraft, the escape slides may be separated from the aircraft for use as life rafts. Consequently, many conventional escape slides are especially designed and constructed to serve well in the dual capacity of escape slide and life raft.
Because of the potential for use of escape slides as life rafts, many conventional escape slides have been constructed principally of nylon fabric which is airproofed with an inner and outer coating of thermosetting polymer such as neoprene. The outer neoprene coating is pigmented to produce a yellow, red or orange color which is highly visible upon the surface of the sea. Such high visibility of the escape slide in its use as a life raft promotes rapid location of the raft and rescue of the passengers.
However, the structure of an aircraft is sometimes damaged during an emergency landing or ditching so that fuel leaks from the aircraft. Such leaking fuel is frequently ignited. While the resulting fuel fire may be of a limited nature so that one or more of the inflated aircraft escape slides are separated from the fuel fire and lead to safety for the passengers, such a fire nevertheless jeopardizes even distant escape slides. Such is the case because a fuel fire may be very intense, generating high temperatures and liberating intense radiant heat energy. The radiant heat energy impinging upon the inflated escape slides rapidly heats both the flexible material from which the slide is made and the inflation gas therein. As a result, the internal inflation pressure may increase at the same time that the slide fabric is heated and weakened. Of course, such a combination of factors eventually results in a breach in the inflated escape slide and rapid deflation.
Ironically, it has been discovered that the high-visibility coloration of conventional escape slides greatly increases the rate at which the inflated slides absorb radiant heat energy from a fuel fire. The radiant heat flux from a fuel fire may be so intense that conventional escape slides are destroyed in just a few seconds time. For example, a conventional escape slide may endure for only 90 to 120 seconds when exposed to a radiant heat flux of 1.5 BTU/ft.sup.2 -sec. The endurance of such a conventional slide may be as short as 40 to 50 seconds if the radiant heat flux reaches a more intense level of 2.0 BTU/ft.sup.2 -sec.
The usual mode of failure of a conventional escape slide when exposed to radiant heat flux is charring of the thermoset neoprene and a localized loss by the nylon fabric of its ability to hold inflation air pressure. Attempts have been made to improve the air holding ability and heat resistance of conventional escape slides by painting them with an aluminized paint. However, these attempts have met with little success. It is believed that the conventional high-visibility pigmented fabric continues to be absorptive of radiant heat energy despite an overcoat of somewhat reflective aluminized paint.
Moreover, a conventional aircraft escape slide may be destroyed at a time and under conditions such that its mere destruction leads to passenger injuries or deaths even though other routes of escape may be available. After witnessing the destruction of an aircraft escape slide, which is an apparent bridge to safety, passengers may be left to escape a burning, smoke filled aircraft by whatever route is open to them. Such a situation promotes panic and rash behavior leading to injuries or death which cool-headed conduct might have prevented. Accordingly, it is desirable that the escape slides of an aircraft endure as long as possible both to provide a route of escape for the passengers and to avoid the panic which may result when an escape slide fails.
Growing recognition of the vulnerability of conventional aircraft escape slides to destruction by radiant heat flux has lead a major airframe manufacturer to express a need for escape slides which are resistant to radiant heat flux. Further, such recognition may result in the promulgation by the F.A.A. of official guidelines and standards for radiant heat resistance of escape slides for commercial passenger aircraft. A precursor of such guidelines is seen in A.S.T.M. draft standard 07.06-12-2 which is applicable to radiant heat testing of fabrics for escape slides.
U.S. Pat. Nos. 3,935,607 and 4,083,070 are believed to relate to inflatable structures; while U.S. Pat. Nos. 2,759,522; 3,092,530; and 3,591,400 are believed to relate to materials which are resistant to radiant heat energy.